The class had a pizza party 3/8 of a pizza was left over and 4/8 of a pizza with other pizza was left over you put them both into a box how much pizza do you have all together

That was not worded very well but I get it ...

If there are 3/8 of one pizza and 4/8 of another when you put them together you add

3 4 7

_ + _ = _

8 8 8

Because 3+4 = 7 and you place that over your denominator

You would have 7/8 of pizza slices total.